Have Stock Music App Ignore All But One Folder?

So I'm mostly satisfied with the stock music app, though I'd probably look for something better if it weren't that it's the only thing that has a gadget on HTC's lock screen.

The only problem that I have is, it finds all the sounds on my phone. So sometimes when shuffling everything, for example, I'll get an audiobook or radio play I downloaded with an app. Or, most frustrating, one of my custom ringtones or notification sounds will pop up in the music shuffle, making me grab for my phone (although I've learned to not be so jumpy when it comes up after an actual song has just ended, it's still annoying). In addition, I use my SD card on different devices, and keep some music in the root folder for listening elsewhere, and those songs get duplicated in the music list.

I've seen a guide to ignoring specific folders using a .nomedia file, but is there a way to have it <i>only</i> look in a /music/ or other folder? Preferably on the embedded memory, not the SD card. For that matter, I can't find any settings for the stock app at all, the menu only gives options for the current song or playlist.

Is there any way to fix this without adding .nomedia to every download/app folder for ever more?